Carried out design, fabrication and testing of dynamically scaled aeroelastic models of typical aircraft wings and satellite launch vehicles in low speed and supersonic wind tunnels. In parallel, developed vibration and flutter analysis of thin panels that included skewed, trapezoidal and tapered thickness plates.

Dynamic Analyses of Wind Turbines: Developed a coupled nonlinear flap-lag-torsion aeroelastic analysis of a horizontal axis wind turbine taking into consideration effects of gravitational loading and earth’s boundary layer, especially for large diameter rotors. Dynamic blade response and parametric resonance instability were investigated systematically for different operating conditions. Limit cycle flutter analysis was carried out using harmonic balance method. Results showed the possibility of sustained limit cycle blade motions at some rotational speeds if large enough disturbance is given to blades (possible with atmospheric gust) (very first study on this topic).

Stall Flutter and Divergence of Wings: Simple wing models were tested in a low speed wind tunnel for nonlinear stall flutter characteristics. Harmonic coefficients were extracted from the free transient vibration data in pre- and post-stall regions. These coefficients are important to develop dynamic stall models.

NASA Ames Research Center (June 1977 to May 1978)National Research Council Post-Doctoral Fellow

Dynamic Analysis of Circulation-Controlled Rotors: Theoretical analyses for flight stability and flutter stability of circulation control rotors in hover were formulated (very first time). The effect of trailing edge blowing on the handling qualities of a helicopter in longitudinal and lateral modes and blade flap-lag flutter stability was examined for different flight conditions and rotor configurations. It was shown that the blowing has a powerful effect on blade stability, which should be considered in rotor design. These key findings were useful in subsequent development of the X-Wing aircraft.

Stanford University (June 1978 to October 1981)Senior Research Associate at NASA/Stanford University Joint Institute of Aeronautics and Acoustics

Dynamic Testing of Full-Scale Rotors in 40 x 80 foot Wind Tunnel: Advanced algorithms were developed on a Dynamic Analysis System (a minicomputer based time series system) for on-line stability measurement of rotors in a wind tunnel. These include: diagnostic blade response and loads, moving-block damping identification, Bode plots and regressing rotor loads analyses. These algorithms were used in various full-scale helicopter rotor tests in the 40 x 80 ft wind tunnel, that include Kaman Circulation Controlled Rotor, Lockheed X-Wing Rotor, Boeing Bearingless Main Rotor, Sikorsky ABC Rotor, and Hughes Advanced Composite Rotor tests. Many of these algorithms are routinely used even today for rotor testing in the 40 x 80 / 80 x 120 ft. wind tunnel (World’s largest wind tunnel).

Aeroelastic Analysis of Advanced Rotors: Flap-lag-torsion flutter of two new rotor configurations, constant-lift rotor and free-tip rotor was investigated. The effect of several design parameters on flutter boundary was evaluated.

Finite Element Analysis of Rotor Blades: Finite element aeroelastic analysis of an elastic blade undergoing moderately large coupled flap, lag, torsion and axial deformations was formulated using Hamilton’s approach. Hover stability was calculated from the normal mode equations. The analysis was initially applied to conventional rotors (articulated and hingeless) and later on was extended to include multiple load-path blades such as BMR blades. This was the very first finite element formulation of a bearingless rotor and formed the basis of modern structural analysis of blades.

Multicyclic Vibration Control: A study was conducted to examine the performance of various active feedback control systems for vibration reduction of helicopters. The controllers studied were: open-loop with off-line identification, closed-loop with off-line identification, open-loop adaptive, and closed-loop adaptive. The on-line identification of model characteristics was performed using a Kalman filter solution. The design implication of different regulators was examined for various flight conditions. This study helped in the selection of a feedback controller for full-scale testing of a rotor system in the 40×80 ft wind tunnel.

University of Maryland (October 1981 – Present)Department of Aerospace Engineering

October 1981 to June 1986 – Associate Professor
July 1986 to Present – Professor
June 1988 to August 1990 – Acting Department Chairman
From October 1991 – Director Alfred Gessow Rotorcraft Center
January 1996 to January 2000 – Minta-Martin Research Professor
From November 1998 – Alfred Gessow Professor
From January 2009 to August 2009 – Interim Department Chairman

Teaching:

Taught the following undergraduate and graduate courses

Flight Structures I & II (Undergraduate)

Vibration & Aeroelasticity (Undergraduate)

Structural Dynamics (Graduate)

Aeroelasticity (Graduate, developed new course)

Helicopter Dynamics (Graduate, developed new course)

Helicopter Theory (Graduate/Undergraduate)

Smart Structures (Graduate, developed new course)

Helicopter Design (Graduate)

Committee member for several Ph.D. and M.S. dissertations in Aerospace, Mechanical, Electrical and Civil Engineering Departments.

Service: Community Service

DUVAL HIGH SCHOOL (P. G. COUNTY)
Member of School Advisory Board, 1989 – 2003

SIKORSKY MINORITY FELLOWSHIP FOR UNIVERSITY OF MARYLAND
Instrumental for 3 Minority Fellowships for engineering students starting from 1993.

Short Courses:

One week course on “Helicopter Aerodynamics and Aeroelasticity” taught at the following organizations (with Professor Alfred Gessow):
Edwards Air Force Base, California, August 1983
The University of Kansas, Lawrence, Kansas, August 1983
NASA Langley Research Center, Hampton, Virginia, Jan. 1984
Patuxent Naval Air Center, Maryland, January 1984
Singer-Link, Binghampton, New York, June 1985